Venetian blinds are very commonly used for shielding window and door openings to block the passage of light and to provide privacy. Venetian type blinds comprise a plurality of horizontal slats (also referred to as louvers or vanes), parallely extending, that can be tilted about a parallel, horizontal axis to open and to close the window blind.
Typically, tilt of such slats is controlled by rotation of a rod attached to a gear mechanism or by pulling on a chain engaged with a gear mechanism. Raising and lowering of the slats is facilitated by pulling a cord attached to a mechanism that engages the cord to lock the location of the slats at a desired elevation.
Conventional blinds incorporate a looped cord having two cord lengths. The cord lengths are attached to a mechanism inside the blind that moves the slats, and either cord length can be pulled to selectively open or close the blind vanes. Such looped cords hang free from one side of the blind, and the necessary length of the looped cord depends on the width of the opening. Blinds for large openings require a looped cord extending to the floor, which creates a potential safety hazard for small children. Also, the cord has the tendency to tangle with adjacent objects and at times also with the rod.
Various mechanisms have been proposed for addressing this issue. For example, electrically powered mechanisms are known for controlling the tilt and elevation of the slats. These mechanisms however require the provision of an adjacent electric socket and further, such mechanisms are relatively complex and expensive. According to an other concept mechanical means are provided for control of the slats. For example, U.S. Pat. No. 5,671,793 discloses a controller for opening and closing Venetian blind vanes over a door or window opening, the mechanism comprising a pull cord that is engaged with a pulley, which is moved with a loop cord selectively engaged with a cord lock attached to a handle. A rotatable switch in the cord lock is rotated, the cord lock grasps the loop cord, and the handle is moved downwardly to pull to loop cord. Such movement operates the pulley and pull cord to raise the blind vanes. When the cord lock is disengaged, the weight of the blind returns the components to the original position. A rotatable tilt switch or combination of rotatable tilt switches are attached to a tilt rod for selectively rotating the blind vanes. All cords are completely enclosed so that looped ends of the cords are not accessible to persons adjacent the window blind.
Another arrangement is disclosed in EP1557524A2 relating to lift and tilt mechanisms for a Venetian blind comprising a plurality of parallel elongated slats and pairs of tilt and lift cords, where the lift and tilt mechanisms comprise a tubular member mounted for rotation with and axial displacement over a drive shaft and guide means for maintaining the lift cords in their proper axial position and for directing the lift cords to the outer circumferential surface of said tubular member, whereby the lift cords upon rotation of said tubular member will become helically wound on or off the circumferential surface of the tubular member resulting in said slats being raised or lowered as the tubular member rotates.